In the production technology for divan and/or chair-beds, it is known of the need to have foldable mattresses designed to assume a first configuration in which part of the mattress is folded in an erect position so as to form the backrest of the divan and the remaining part of the mattress is folded onto itself so as to form a double layer corresponding to the seat of the divan itself.
It is also known that one of the main problems connected with the use of these mattresses is, in fact, that, in order to fold the mattress onto itself and at the same time limit the overall thickness thereof inside the divan structure, it is necessary to provide mattresses of limited thickness which prove to be not very comfortable particularly when used for sleeping purposes. In fact, the user is no longer supported by a double layer due to folding over. That is when the divan is used as a seat, the actual relatively thin thickness of the mattress does not fulfil entirely its function of providing a springing and damping action.
In order to solve this problem, mattresses of greater thickness have also been proposed, however, the mattress is usually formed of independent parts joined together by additional elements such as zip fasteners and the like which, albeit being functional for folding of the mattress, become undesirable elements when the mattress is opened out for use as a bed. In this configuration, in fact, the additional elements produce bumps and/or dips which do not permit a comfortable supporting action.